1. Field of the Invention
The present invention relates generally to the biomedical arts, and, in particular, to a device for use in conjunction with cuff electrodes for stimulating nerves.
2. Description of the Related Art
Functional electrical stimulation of the nervous system has been shown in recent years to offer great hope in restoring some degree of lost sensory and motor function in individuals with severe spinal cord injuries. Ways in which functional electrical stimulation of peripheral nerves can be utilized to restore a particular function include: (1) the use of surface electrodes to activate the nerves in the general region of interest; (2) the use of intramuscular electrodes, also to activate the nerves in a general region; and (3) the use of nerve cuff electrodes placed about specific nerves of interest and used to activate them specifically. The third alternative offers advantages over the first two in that it requires the least amount of stimulating current and hence charge injected into the tissue. In addition, it allows easy excitation of entire muscles rather than parts of muscles, a common situation for the first two categories. Because the use of nerve cuff electrodes requires delicate surgery, they are usually contemplated only when: (1) excitation of specific isolated muscles is desired; or (2) the generation of unidirectional action potentials is required.
Various prior art cuff electrodes have been utilized in the past to apply electrical stimuli to nerves. U.S. Pat. No. 4,602,624 is directed to a cuff electrode which encircles a nerve trunk with at least one electrical energy conductive member held against the tissue and a non-conductive sleeve extending to either side of the conductive member. This cuff is a self-curling sheet which is biased to curl into a light overlapping cylindrical spiral around the nerve trunk. U.S. Pat. No. 5,324,322 is directed to a cuff electrode having a spiral cuff portion which is connected to a spiral lead portion. The spiral cuff portion is coiled around a nerve, while the spiral lead portion is used to couple the device to an appropriate power source. U.S. Pat. No. 5,505,201 is directed to a helical nerve cuff electrode which curls into a helical spiral around a nerve fiber as it is ejected from a carrier tool.
While these spiral cuff electrodes are very effective in delivering the desired electrical pulses to selected nerves, they all suffer from some deficiency. The manner in which these electrodes are coupled to the power sources often makes the installation of these electrodes a difficult and very delicate procedure. Lead wires which attach the cuff electrodes to the power source must be bonded to each electrode by welding, soldering or using special conductive epoxies. These connections are often very difficult and labor intensive to make, requiring the time and talent of a skilled fabricator, and increase the physical size of the electrodes. In addition, these connections are subject to mechanical failure due to repeated flexure of the electrodes, and any failure at the connection of the electrode and lead requires removal of the electrode and the implantation of a new electrode.
Finally, the conductor leads themselves must travel from the electrodes to the power source. These leads must often be anchored by a strain relief to protect the connections from physical movement. Also, if there are several electrodes to be implanted in the same area of the body, the number of leads required to connect the power source to the electrodes will contribute significantly to the overall size of the implanted system, making installation more difficult.
The present invention provides a new and improved nerve cuff electrode carrier which overcomes the above referenced problems and others.